Automotive windshield wiper systems typically use a pair of motor driven wiper blades to clean the windshield. In most systems, a single motor is used with a mechanical linkage between the wiper blades so that the single motor provides simultaneous, synchronous reciprocation of the two wiper blades. Automotive vehicles also typically include a windshield washer system that sprays washer fluid onto the windshield to aid in the cleaning of the windshield by the wipers. The washer system can include a washer fluid reservoir to store the washer fluid, a pair of nozzles to spray the fluid onto the windshield, and a pump to supply the washer fluid to the nozzles. While these washer systems are commonly located in the engine compartment near the windshield wiper system itself, integration of the washer system and the windshield wiper system into a compact assembly can be difficult because of the moving mechanical linkages used to drive both wipers from a single motor.
Windshield wiper systems have been designed that utilize separate electric motors for each of the wipers. See, e.g., U.S. Pat. No. 4,585,980 to Gille et al., U.S. Pat. No. 4,665,488 to Graham et al., U.S. Pat. No. 4,900,995 To Wainwright, and U.S. Pat. No. 5,252,897 to Porter et al. While eliminating the mechanical linkage between the wipers, these dual motor system have at times been disfavored because operation of the two motors must be properly coordinated to prevent collisions between the two wipers. Coordination of the motors has been accomplished using position feedback by sensing, for example, the position of each motor's armature or by using position sensors on the wiper levels or the windshield itself, as in U.S. Pat. No. 5,157, 314 to Kuhbauch.
In the field of motor controllers generally, motor position feedback has been used in brushless dc motors for commutation of the motor windings. This has sometimes been done using Hall Effect sensors, as in U.S. Pat. No. 4,680,515 to Crook, U.S. Pat. No. 4,723,100 to Horikawa et al., and U.S. Pat. No. 4,897,583 to Rees. The output of these Hall Effect sensors have also been used along with a clock oscillator to produce position and tachometer signals for operational control of the motor. See, for example, U.S. Pat. No. 4,415,844 to Mendenhall et al. and U.S. Pat. No. 4,717,864 to Fultz.
While suitable for use in windshield wiper systems, the use of the above-noted brushless dc motor controllers in a windshield wiper system that uses separate position sensors for coordination of the wipers can result in an unnecessarily complicated design.